Before taking someone into custody, the police must determine if they can establish probable cause that the person committed a crime. Under the Fourth Amendment, they must have evidence that reasonably demonstrates the suspect committed a criminal offense in order to arrest them. They may need to conduct a 
pre-arrest criminal investigation to establish probable cause to make an arrest.
If you are a suspect in a criminal investigation or are facing criminal charges, it can be helpful to understand how the police and prosecutor conduct these investigations. It can help you know what to expect in your case and may assist in developing a defense strategy to fight the charges if you are arrested. Our Charlotte criminal defense lawyer explains more below.
How the Police Perform Criminal Investigations
The scope of a criminal investigation can vary depending on the type of criminal activity being investigated. In some cases, such as reckless driving charges, a fight at a bar or other location, or domestic violence, the police may not need to conduct any investigation other than at the scene before arresting someone.
Similarly, the length of time the police will engage in a pre-arrest investigation will depend on the seriousness and complexity of the crime. Some can take days, weeks, or a year or more to complete. Here are some ways that law enforcement officials and prosecutors conduct an investigation before making an arrest.
Collecting Physical Evidence
One way that the police can build a case against a suspect is through the collection of physical evidence. A detective trained in how to investigate more serious crimes could be assigned to the case. They could go to the crime scene to look for physical evidence, such as a weapon, bloodstains, fibers, footprints, fingerprints, and more. They may take photographs and measurements or send certain samples, such as blood samples or fibers, to a lab for testing.
The police must properly collect and preserve the evidence they obtain in a criminal investigation. If they do not follow required procedures, the evidence could become contaminated or otherwise not be considered valid and may be ruled inadmissible in a criminal case.
Conducting Interviews
Another pre-arrest investigative tool the police could employ is to interview the victim of the alleged crime and witnesses. They would speak to anyone that they believe has helpful information, which could include a suspect’s co-workers, family, friends, and neighbors.
Detectives could also bring in a suspect for questioning. Unless the individual is in custody, law enforcement officials do not have to give them their Miranda warnings and can use any statements made against the accused.
Engaging in Surveillance
Depending on the crime being investigated, a team of detectives or police officers could engage in surveillance of a suspect or others who could have useful information. They may engage in surveillance at various times in an investigation.
Searching Social Media and Other Records
Detectives could also search a person’s social media sites or other websites where individuals discuss potential crimes with others for evidence that a crime was or is about to be committed. They may also obtain a warrant to get an individual’s cell phone, financial, or other records from businesses or other parties.
Going Undercover
Law enforcement officials sometimes go undercover as part of their investigation of a possible crime. This is not uncommon in drug offense, p*rnography, or other serious felony investigations.
